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Post by PeterW on Aug 17, 2006 20:17:03 GMT -7
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Post by thecrypt on Jan 20, 2007 22:59:48 GMT -7
I saw that, but I wouldn't spend that much on it when I can spend the same for a cone system that is much nicer.
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Post by ThomasW on Jan 20, 2007 23:08:07 GMT -7
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Post by thecrypt on Jan 21, 2007 1:16:39 GMT -7
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Post by arande2 on Mar 15, 2007 15:17:19 GMT -7
If you covered the wall with them I'm sure you could do some major SPL at 1hz.
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Post by htnut on Mar 15, 2007 21:23:07 GMT -7
When I try out a speaker with my signal generator it is fun to watch it do a 1 hz excursion. Trust me, nothing much will come of that sort of cone movement.
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Post by chrisbee on Mar 16, 2007 0:33:39 GMT -7
Do the card test.
Wave a postcard slowly. Hear anything? Nope.
Get a nice big board. Wave it slowly. Hear anything? Not much but now your hair is moving.
Now go and stand in front of a fan and move your postcard around in the breeze. Now you can hear something. Turbulence.
Very low frequencies are all about lots of air movement.
Let an 8 x 4 board drop flat onto a smooth surface. That's air movement too.
Now all you need to do is find a way to make a few 8 x 4s vibrate while tightly sealed into the wall surface.
Or use a fan with variable pitch blades.
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Post by htnut on Mar 16, 2007 5:41:30 GMT -7
So 25 Q18s are equivalent to one sheet of 4x8. However they wont move very far, two inches maybe. What do we get when we move the 4x8 two inches.
Waving the bits of flat panel does not emulate a cone with very limited movement. So instead of waving the big piece of cardboard just push it in and out by two inches total movement and see if your friends hair moves at all even one meter away. Probably wouldn't move his hair with the 4x8 if you restrict the movement to two inches.
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Post by arande2 on Mar 16, 2007 20:19:42 GMT -7
They need to make a giant sine generator where you install a 30x10 ft sheet of titanium with an extreme excursion surround (a few meters) into a wall of a sealed room. You could hook a bunch of high HP motors hooked to gears to move it back in forth at different speeds. You could mess with the power going to the motors to change the speed it moves at or even maybe use some sort of relay system with an amplifier hooked so that you can play a tone and it will come out on the sheet. It would be very limited...since the excursion would never change, so while 10hz may shake you, 20hz would shake you a lot harder and so on.
Well...I guess a few meters of excursion would require some extremely powerful motors and thick titanium. Still, I'd like to see what SPL levels that would create if you had enough reinforcement and motor strength to get 5 meters excursion at 10khz...it would probably catch stuff on fire, right? Or am I thinking about it all wrong?
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Post by PeterW on Mar 16, 2007 22:49:14 GMT -7
10 khz...... im almost sure that physics would require some insane power and strenght levels. Ahem, millions if not billions of horsepwer.... i dont think there is any substance that could hold up to that excursion at 10 khz with a 30x10 foot sd.... you would probably not be able to contain the rearwave let alone the frontwave..... the building would colapse instantly, and the beaming due to the sd would be horriffic. All forms of matter, would be ripped apart instantly, and everything would turn into dust for hundereds of meters / feet..   |
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Post by chrisbee on Mar 17, 2007 0:04:16 GMT -7
Since we are fantasizing a bit here... ;D A slightly conical polystyrene foam sheet the size of the end wall reinforced with carbon fibre and driven by and supported on a central pneumatic cylinder would produce considerable output and have a stroke of any length you chose. Pneumatics are fast acting and can tirelessly repeat so 10Hz should be possible. Whether you could control the frequency with some sort of programmable electromagnetic air valve I don't know. It would be far easier just to keep adding conventional drivers (and amps) to an IB. Most rooms can manage 4 x 18" drivers in the height of the ceiling. How many 8 x 18" opposed driver manifolds can you slot into the width of your end wall? At least 8 manifolds? Well 64 x 18" drivers are going to move some serious air! 64 drivers x $300 each is still under $20k! Probably get a nice discount which will pay for your amps and MDF. This is one serious world class subwoofer for so little real money.  What's holding you back?  |
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Post by arande2 on Mar 17, 2007 16:15:12 GMT -7
Muahahaha! SSSSSS
I bet it would still do some crazy SPL at 100hz!
What is holding us back? HMMMM.... Crazy Subwoofer Man (as opposed to Crazy Cat Lady) in the future...?
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Post by htnut on Mar 17, 2007 20:17:37 GMT -7
OK F = m a
So for 10 hz and one meter of travel, I will keep it to one half meter each way about center, and with some foam carbon fiber composite here is an approximation. We will neglect the weight of the piston and rod in the actuator for now.
The foam could be as little as 4 pounds per cubic foot. Most likely to keep any sort of rigidity at all in a 30 by 10 foot panel the composite skins would have to be space at least 4 inches apart. So we have one cubic foot of foam every three square feet. We have 300 square feet in our driver so that is one hundred pounds.
Now we need skins. About 1/8 inch should do on each side. With a weight of about 70 pounds per cubic foot and with 1/4 inch material every 48 square feet is a cubic foot. Rounding off and giving you the benefit of the doubt we now have about 420 pounds of composite skins.
520 pounds is 16.25 slugs which is the mass of our diaphragm.
Acceleration would have to be 41 g's more or less
That makes our force required about 1880 pounds to start the sine wave at 10 hz.
Lets say we use hydraulics at 2000 psi, then our cylinder would have a volume of approximately 35 cubic inches for the meter stroke. And we would be filling and emptying that cylinder every tenth of a second. So we would be pumping about 29 gallons per minute. A quick search says we would need about a 30 horsepower unit more or less.
Maybe that Thigpen isn't so expensive after all.
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Cozmo
New Member
Bassahaulic
Posts: 10
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Post by Cozmo on Feb 6, 2008 13:33:30 GMT -7
OK F = m a So for 10 hz and one meter of travel, I will keep it to one half meter each way about center, and with some foam carbon fiber composite here is an approximation. We will neglect the weight of the piston and rod in the actuator for now. The foam could be as little as 4 pounds per cubic foot. Most likely to keep any sort of rigidity at all in a 30 by 10 foot panel the composite skins would have to be space at least 4 inches apart. So we have one cubic foot of foam every three square feet. We have 300 square feet in our driver so that is one hundred pounds. Now we need skins. About 1/8 inch should do on each side. With a weight of about 70 pounds per cubic foot and with 1/4 inch material every 48 square feet is a cubic foot. Rounding off and giving you the benefit of the doubt we now have about 420 pounds of composite skins. 520 pounds is 16.25 slugs which is the mass of our diaphragm. Acceleration would have to be 41 g's more or less That makes our force required about 1880 pounds to start the sine wave at 10 hz. Lets say we use hydraulics at 2000 psi, then our cylinder would have a volume of approximately 35 cubic inches for the meter stroke. And we would be filling and emptying that cylinder every tenth of a second. So we would be pumping about 29 gallons per minute. A quick search says we would need about a 30 horsepower unit more or less. Maybe that Thigpen isn't so expensive after all. This post rules. I love it when someone breaks things down with knowledge. haha I guess the next step here is to determine that actual output of this hydraulic wall driver and see what it would take to equal it. |
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